| Pentadrone | 2 | Construct | Large | 16 | 32 | | lawful neutral | | Monster Manual | | | | | | |
| Pegasus | 2 | Celestial | Large | 12 | 59 | fly | chaotic good | | Monster Manual (SRD) | 18 | 15 | 16 | 10 | 15 | 13 |
| Panther | 0.25 | Beast | Medium | 12 | 13 | | unaligned | | Monster Manual (SRD) | 14 | 15 | 10 | 3 | 14 | 7 |
| Owlbear | 3 | Monstrosity | Large | 13 | 59 | | unaligned | | Monster Manual (SRD) | 20 | 12 | 17 | 3 | 12 | 7 |
| Owl | 0 | Beast | Tiny | 11 | 1 | fly | unaligned | | Monster Manual (SRD) | 3 | 13 | 8 | 2 | 12 | 7 |
| Otyugh | 5 | Aberration | Large | 14 | 114 | | neutral | | Monster Manual (SRD) | 16 | 11 | 19 | 6 | 13 | 6 |
| Orthon | 10 | Fiend (devil) | Large | 17 | 105 | | lawful evil | | Mordenkainen's Tome of Foes | | | | | | |
| Orog | 2 | Humanoid (orc) | Medium | 18 | 42 | | chaotic evil | | Monster Manual (BR) | 18 | 12 | 18 | 12 | 11 | 12 |
| Orcus | 26 | Fiend (demon) | Huge | 17 | 405 | fly | chaotic evil | Legendary | Mordenkainen's Tome of Foes | 27 | 14 | 25 | 20 | 20 | 25 |
| Orc war chief | 4 | Humanoid (orc) | Medium | 16 | 93 | | chaotic evil | | Monster Manual | | | | | | |
| Orc red fang of shargaas | 3 | Humanoid (orc) | Medium | 15 | 52 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Orc hand of yurtrus | 2 | Humanoid (orc) | Medium | 12 | 30 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Orc eye of gruumsh | 2 | Humanoid (orc) | Medium | 16 | 45 | | chaotic evil | | Monster Manual (BR) | 16 | 12 | 16 | 9 | 13 | 12 |
| Orc claw of luthic | 2 | Humanoid (orc) | Medium | 14 | 45 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Orc blade of ilneval | 4 | Humanoid (orc) | Medium | 18 | 60 | | chaotic evil | | Volo's Guide to Monsters | | | | | | |
| Orc | 0.5 | Humanoid (orc) | Medium | 13 | 15 | | chaotic evil | | Monster Manual (SRD) | 16 | 12 | 16 | 7 | 11 | 10 |
| Oni | 7 | Giant | Large | 16 | 110 | fly | lawful evil | | Monster Manual (SRD) | 19 | 11 | 16 | 14 | 12 | 15 |
| Olhydra | 18 | Elemental | Huge | 18 | 324 | swim | neutral evil | | Adventures (Princes of the Apocalypse) | | | | | | |
| Oinoloth | 12 | Fiend (yugoloth) | Medium | 17 | 126 | | neutral evil | | Mordenkainen's Tome of Foes | | | | | | |
| Ogremoch | 20 | Elemental | Gargantuan | 20 | 526 | | neutral evil | | Adventures (Princes of the Apocalypse) | | | | | | |
| Ogre zombie | 2 | Undead | Large | 8 | 85 | | neutral evil | | Monster Manual (SRD) | 19 | 6 | 18 | 3 | 6 | 5 |
| Ogre howdah | 2 | Giant | Large | 13 | 59 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Ogre chain brute | 3 | Giant | Large | 11 | 59 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Ogre bolt launcher | 2 | Giant | Large | 13 | 59 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |
| Ogre battering ram | 4 | Giant | Large | 14 | 59 | | chaotic evil | | Mordenkainen's Tome of Foes | | | | | | |